While on the subject of consistency, one should avoid doing having code that does more extra work that is not directly related for why it was written. It should be like a conversation with parts of a conversation focusing upon the subject being discussed.

Example: BrowserUk wrote this, my wife bought a new car today and I hate my co-workers, excellent article and I enjoyed reading it.

This is a tough to read but is common problem among programmers.

A more practical example would be a function that mix SQL with business logic with HTML. Doing all three at the same time makes it hard to debug and reduces the portability of the code. You cannot,

Use the code outside of a program that does not need HTML.

Use the code outside of a database because you only need the business logic.

Use the code to just get data because the business logic is invalid in that situation.